A typical structure of a shoe for a swash plate type compressor is disclosed in, for example, U.S. Pat. No. 4,329,913 of Nakayama et al. The compressor has a pair of horizontally axially aligned cylinder blocks which form a combined block. Inside the combined block are formed axially extending cylinder bores, and the cylinder block is closed at both ends by front and rear housings via valve plates. Passing centrally through the combined block, a drive shaft is rotatably supported by a suitable bearing means. To the middle of the drive shaft is fixed a swash plate operatively connected, via ball bearings and shoes, to double acting pistons slidably fitted in the cylinder bores. Thus, the rotating motion of the swash plate causes the reciprocal compressing motion of the pistons within the cylinder bores. The front and rear housings have refrigerant suction chambers and refrigerant discharge chambers, which are interconnected with the cylinder bores and are connectable to an outside air conditioning system by means of appropriate refrigerant flow pipelines. The above-mentioned respective shoes are normally shaped as a round plate having, at one side thereof, a flattened face slidably in contact with the face of the swash plate. At the other side of the round plate, each shoe has a recess for receiving therein a part of the ball bearing engaged with a spherical recess of the piston.
Another conventional swash plate type compressor employs different type of shoes, each having, at one side thereof, a flattened face slidably in contact with a swash plate, and at the opposite side thereof, a spherical raised portion directly engaged with a double acting reciprocatory piston without the intervention of a ball bearing. Thus, the swash plate is operatively connected to the piston by only the shoes alone, eliminating the need to provide ball bearings.
With the above-mentioned conventional swash plate type compressors, there is a recent practical requirement such that the compressors are operated at a high compression ratio so as to increase a refrigeration efficiency of the airconditioning system. As a result, it is necessary that the shoes for the swash plate type compressor have sufficient resistance to seizure under a running condition of the compressor at a high compression ratio. One proposal for satisfying this necessity is to employ shoes made of a material having a sufficient resistance to seizure, such as various kinds of ceramic, and hard metal. However, these seizure-resistant materials usually are not easily machined, and therefore, a satisfactory accuracy of the dimensions of the shoes cannot be obtained. Accordingly, the use of these seizure-resistance materials for the shoes is considered impracticable. At this stage, from the past experience of the present inventors, it is understood that although the flattened face of the shoe in contact with the swash plate must resist seizure, the other recessed or raised side of the shoe may have less resistance to seizure. It is understood that machining the flattened face of the shoe is easier than machining the recessed or raised side of the shoe. Consequently, the present inventors have contrived to produce shoes having a flattened face made of seizure-resistant material and in contact with the swash plate face, and a recessed or raised side made of material having less resistance to seizure but easily machined.